The invention in general relates to a system for reading a printed code in order to convert this code into a signal of a different nature, notably into an audio signal. Systems of this kind are sometimes known as "talking books". The medium may be in a form other than a book (for example, a single sheet of paper). The term "printed" is to be understood to include also other graphic techniques, such as offset and the like. The medium contains information which is suitable for visual reception, for example, in the form of text or pictures. Furthermore, there is provided a code unit (or several code units), for example, a code field which is linked to a part of the "non-code" information by way of its location. Random access to the code is possible to a given extent, for example, in that a sheet of the carrier comprises a plurality of code fields which can be selected by a user "at a glance". The content of the audio signal may be very diverse, such as speech (e.g. in the case of a text printed in a foreign language), music, or background sounds for the display of an occurrence. The invention, however, notably does not relate to sound films with added sound which has to be optically scanned, because sequential scanning is then present for sound as well as pictures; the scanning is then a mechanical scanning which is combined for image and sound, so mutually synchronized in the time. The invention neither concerns systems comprising, for example, a rotating video disc (VLP), which also have a mechanical drive with a synchronization of picture and sound which is fixed in the time, because otherwise separate detectors would be required for sound and picture. Moreover, the video disc does not contain a "visible" picture, but only the code thereof.
The invention, however, notably relates to a device for generating audio signals on the basis of code representations which are derived from a printed carrier and which are present on a visually selectable zone of the surface of the carrier, comprising:
a. first means which are suitable for manipulation and which serve for the selective and optical scanning of said zone and for deriving code signals from the code representations present therein; PA0 b. second means for receiving and processing said code signals and for developing reproduction control signals therefrom; PA0 c. third means for sequential actuation of acoustic generator means under the control of signals originating from said second means. PA0 b1. an intermediate memory having a data input which is connected to an output of the first means; PA0 b2. a synchronization mechanism for deriving synchronization signals from the signals of the code representations and for controlling the storage of code signals in the intermediate memory by means of these synchronization signals; PA0 b3. a clock for reading code signal information stored in the intermediate memory and for presenting this information to the third means via an output of the second means. PA0 a1. a scanning device with an optical display device for displaying said zone on an optically sensitive element, whose dimension is larger than the value corresponding to the image of said predetermined dimension; PA0 a2. a mirror device for visual detection of the correct positioning of said first means by coincidence of an image of said zone and a predetermined sector of said scanning device; PA0 a3. a scan sequence generator for controlling a scanning cycle of said optically sensitive element.
A device of this kind is known from U.S. Pat. No. 3,474,194. This specification pays attention to the problem which arises when a large bandwidth of the sound is desired, even though the printing quality (in bits per unit of length) be limited. It would also be undesirable if a high (and constant) speed were required during scanning. According to the known technique, the carrier is scanned in a continuous motion by means of a scanner which is moved by hand, reproduction taking place simultaneously with the scanning. Any low frequency is directly stored on the carrier. If a high frequency is to be reproduced, the carrier contains only a signal of low frequency which is assigned to said high frequency. The audio frequency is recovered again (as a sum frequency) by modulation with a higher frequency produced by the system. Thus, a constant and fixed scanning speed is required. Moreover, the described system is very elementary: repeats and similar functions are not possible.